Abstract: Modern rice (Oryza sativa L.) combinations, like the new super hybrid rice combinations “II Youhang No. 1” and “II Youhang No. 2”, have high yield potentials. However, the underlying high-yield mechanisms of these rice combinations have remained largely unclear. In the present study involving super hybrid rice “II Youhang No. 1” and “II Youhang No. 2 ” combinations, sink, source, flow of these combinations were analyzed in relation to physiological mechanisms of super high-yield formation. The study showed that during grain-filling, photosynthetic parameters such as chlorophyll content (SPAD), net photosynthetic rate (Pn), and chlorophyll fluorescence parameters such as F_v /F_m, F_v /F_o, q_p of flag leaves of two super hybrid rice combinations were significantly higher than those of the control combination “Shanyou 63”. Super hybrid rice combinations exhibited longer filling time of inferior gains and better filling effect over “Shanyou 63”. Sink capacity, sink filling ability and transportation percentage of matter in stem and sheath in super hybrid rice combinations were also significantly higher than those in “Shanyou 63”. The results suggested that super hybrid rice possessed stronger source/sink activity and higher flow efficiency than “Shanyou 63”. Furthermore, “II Youhang No. 2” had higher transportaiton percentage of matter in stem and sheath and sink filling ability, and better yield performance than “II Youhang No. 1”.